/ Dictionary / Index S Sixtus IV: Meaning and Definition of Find definitions for: Sixtus IV Pronunciation: [key] (Francesco della Rovere) 1414–84, Italian ecclesiastic: pope 1471–84. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Sixtus III Sixtus V Related Content Daily Word Quiz: cetacean Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language